Oil in the cylinder

My engine a Lycoming 320 used a liter of oil in the last two hours.
I pulled the plug and oil ran out. The bottom plug was soaked in oil. The last flight it ran fine, made the normal amount of power.
Pulled the valve cover and there was not an unusual amount of oil in it. Checked the drain tube, not blocked.
Checked compression good, same as the other three.

Puzzled, how did the oil get past the rings if the compression is normal?

Could a valve guide seal leak that much??

Ray
Grumman Cheetah, OM

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Originally Posted by raytoews

My engine a Lycoming 320 used a liter of oil in the last two hours...
Puzzled, how did the oil get past the rings if the compression is normal?

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First guess - broken oil rings. I had two a customer and a hangar mate have broken oil rings in their O-235 and O-360 Lycoming within a couple of weeks of one another - very strange. Lycoming said that it's not common, but it does happen. The first sign on the O-360 was huge power loss and vibration - on the O-235, it was using 4 quarts of oil in an hour and a half.

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Originally Posted by raytoews

Could a valve guide seal leak that much??

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I'm not an engine expert, but that seems unlikely - I think you'd see other symptoms before that if the guide was that loose.